Photographic printing paper



Patented June 25, 1940- Edith eyde, Gologne-Nlehl, Geny, gnor,

me assi i of Delaware WW1 to General he a w Coration, New Worn, N. Y... a coma- No g. application retry ill, race, se-

iilaahllw No. 189,762. lln Germany Febmary l5,

The present invention relates to an improvement in the production of photographic prints.

Photographic papers have a tendency to adsorb and thus to retain sodium thiosulfate from 5 the fixing baths and the soluble silver salts produced by the fixing operation. This phenomenon on the one hand aflects the permanence of the photographic print since the retained salts gradually react with the silver image to form silver sulfide and the silver salts also gradually decompose into silver sulfide and thus impart a yellow tint to the paper; on the other hand the phenomenon leads to a more or less pronounced coloring of the whites in the toning of the print, particularly with a sulfide or a selenide, in consequence of the intensely colored silver salts which are formed.

The present invention is based on the observation that the barium sulfate used for whitening the paper is primarily responsible for the undesirable retention of the compounds or salts.

Precipitated barium sulfate has as is known the tendency to adsorb metallic salts (for instance Bach, MgClz or FeCla) and other compounds particularly substances having a high molecular weight such as dextrin which itself has a strong adsorbing tendency (see, for instance, Marc, Zeitschfrit fiir physikalische Chemle, 75, 710, 1911 and 81, 641, 1913). Moreover, it is known that the adsorbing a substance may be afiected by adding a further component. The adsorbing Congo red by means of cellulose, for example, is intensely reduced by adding phosphate ions. It has also been proposed to remove mangano ions which are adsorbed by precipitated manganese dioxide with the aid of solutions of ferrous salts because manganese dioxide is capable of adsorbing ferro ions more intensely than mangano'ions (Geloso, Ann. Chim. 6, 352, mt 1926).

It is one object of my invention to provide a photographic element which comprises a paper layer and an emulsion layer, at least one of said layers, containing an effective amount of a substance capable of compensating the absorptive power'of constituents of said paper.

Another object of this invention resides in the provision of a photographic element which comprises a paper layer, a baryta layer, and an emulw sion layer, one of said layers containing an effective amount of a substance having the property described above.

Further objects will be apparent from the disclosure following hereinafter. 55 Particularly suitable for the purpose of the present invention are the salts of the rare earths. It is noted that it is known that the hydroxides of the rare earths, the salt solutions of which as well known easily hydrolyze, are capable of adsorbing many substances.

It is immaterial at what stage in the manufacture and preparation of the paper these salts are allowed to act upon the barium sulfate. They may be added directly to the barium sulfate grounding or to the emulsion, from which they gradually migrate to the barium sulfate. The desired effect may also be obtained by using such salts in an intermediate bath following the development or as an addition to the fixing bath or even in a separate bath after fixing but before washing. The washing of the paper raw material which may contain the barium sulfate as filling agent may be improved by the substances so that it is advantageous to add them in the preparation of the paper. However, it is W also practicable to soak the'finished paper material with a solution of the substance.

It will be understood that in addition to the substances hereinbefore named there is a number of further substances which have the de- 25 sired action. However, the use of these substances is in part restricted since it is necessary that there should'be no coloration of the paper material or the barytes' and that the substance should not have an unfavourable effect on the photographic emulsion. l

The following examples illustrate the invention:

(1) To 1 liter of a gelatin solution containing barium sulfate such as is used for coating the photographic paper, there are added 3 grams of lanthanum chloride.

(2) To a photographic emulsion there are added per liter 2 grams of cerous sulfate and the emulsion is applied to the paper in the usual d0 manner.

(3) The photographic material is treated after development in a bath of the following composition Water -cc. 1000 M Glacial acetic acid cc. 10 Thorium nitrate -grams 10 amount of a rare earth compound effective to suppress the adsorptive capacity of the barium sulfate for thiosulfates.

2. A photographic element comprising a paper layer, a superimposed barite layer and a lightsensltive silver halide emulsion layer on said barlte layer, at least one of said layers contain- 2 l a l 2,205,756

EDITH WEYDE. 

